The conventional warning light bars being used currently are such warning light bars that use LEDs as light sources. This warning light bar usually includes a warning light body, a plurality of LED light units disposed at the front and the back ends of the light body, lenses that correspond to the LED light units, and supporting legs connected to the bottom of the light body for connecting to the vehicle. On the left and right sides of the light body, a light unit seat is connected, respectively. An end cover and a plurality of LED light units are coupled onto the light unit seat. However, the corners of above warning light bar are unable to emit light, causing the illumination range of the warning light to be restricted. In addition, the brightness of light spots, which are formed by the light from light sources transmitting through lenses, is still not sufficient. This is because a portion of light would be lost during refraction, which causes a waste of luminous energy. In view of the requirement of coupling, bolts are used as coupling elements, such that the thickness of the warning light bar cannot be further reduced. The thickness of current warning light bar exceed 50 mm, since the brightness of the warning light is subjected to restriction of the height of light reflecting plate and the whole structure of the light. The thinner the warning light is, the more the brightness of the warning light would be restricted. On the other hand, in order to ensure the luminous efficiency, the thickness of the warning light bar cannot be further reduced. However, the thicker the warning light is, the heavier it would be. Then higher fastness is required when it is being mounted. This is also a reason that the thickness of current warning light cannot be reduced.